In radio transmission and reception systems, a radio receiver is typically confronted with a multicarrier signal, i.e., a signal comprising a plurality of carrier signals having different signal characteristics, such as different frequencies. Due to variations in broadcast strength and the different locations from which they are broadcast, the respective carrier signals of a multicarrier signal arrive at a particular radio receiver with varying strengths. The difference in strength between the highest and lowest constituent carrier signals defines the dynamic range of the multicarrier signal.
FIG. 1 depicts a schematic diagram of the front-end of a conventional radio receiver. Receiver 100 receives the broadband signal via antenna 101. Bandpass filter 105 takes the received broadband signal and passes only the multicarrier signal, eliminating signals whose frequencies are outside the multicarrier range defined by the filter. The multicarrier signal is mixed down by mixer 117 cooperating with local oscillator 125 and sent to a second bandpass filter 119. Bandpass filter 119 selects the particular frequency band or bands of interest which form the output signal. Typically, the utility of a radio receiver is limited by the dynamic range of the receiver components that process the signals of interest. More specifically, the dynamic range which the radio receiver can satisfactorily process is usually limited, at one extreme, by noise, and at the other extreme, by the inherent physical characteristics of mixer 117. If the dynamic range of mixer 117 is too low, the mixing of a multicarrier signal with a wide dynamic range can introduce undesirable intermodulation products into the output signal. When the radio receiver forms a portion of a cellular communications system, the wide variation in signal power levels creates particular signal processing problems. Therefore, there is a need in the art for signal processing elements which can process multicarrier signals with wide dynamic ranges without introducing distortion in the resultant output signal. Such signal processors could advantageously be employed in radio receivers and cellular communications systems to reduce the dynamic range of multicarrier signals. In particular, such signal processors could be employed in CDMA cellular communications systems to substantially reduce or eliminate signals which are not spread-spectrum-modulated.